habitable zone

A habitable zone (HZ) is a region of space where a planet
can hold liquid water (i.e., surface water),
which is considered a prerequisite for life as we know it.

In particular, a circumstellar habitable zone
(CHZ) is the zone around a star with this potential.
The concept was introduced in 1953 and to some extent
is now less popular than in the past. The terms
liquid water zone and liquid water habitable zone
are also used, but other criteria
may be of use such as for the size/frequency of stellar flares, etc.
The outer edge is basically the system's snow line.

Regarding the solar system, different studies suggest
different boundaries, but the region from Venus to
Mars is considered a rough approximation.

A galactic habitable zone is a region of a galaxy
suited to life as we know it, i.e., sufficient metallicity, and
an advantageous number of catastrophic events,
i.e., supernovae, gamma-ray bursts, etc.
Some supernovae may be an advantage to the extent
that they contribute to metallicity and star formation.

Some have considered radiation (alpha, beta, gamma) regarding
habitable zones, i.e., just a little to assist evolution through
mutation but not enough to prevent development. In my mind, this
may be a bit over-oriented toward the sort of life on Earth.